Born Oct. 20, 1908, in Yamaguchi Prefecture. Leading figure in the Japanese communist movement; member of the Communist Party of Japan (CPJ) since 1931.
A peasant’s son, Miyamoto graduated from the economics faculty of Tokyo University in 1932. He was active in the student movement during 1930–32, and in the work of the Student Social Science Federation. He was a member of the All-Japan League of Proletarian Art and in 1932 worked in the propaganda and agitation section of the CPJ Central Committee.
In 1933, Miyamoto was elected to membership in the Central Committee, as well as to the party’s Secretariat and Politburo. That same year he was arrested and imprisoned until 1945. He has been a member of the CPJ Central Committee from 1945 and since 1946 has been a member of the Politburo as well, the latter being transformed in 1955 into the Presidium of the CPJ Central Committee.
Miyamoto was editor of the CPJ theoretical organ, Zenei, during 1946–49, and chaired the Party Control Commission during 1947–50. He was a secretary of the CPJ Central Committee from 1955 until 1958 and editor in chief of the newspaper Akahata until 1957. During 1958–70 he was general secretary of the CPJ Central Committee. Miyamoto became a member of the Permanent Bureau of the Presidium in 1964 and chairman of the Presidium in 1970.